1. Field of the Invention
The present invention relates to a photoelectric converter for converting a received optical signal to an electric signal, an image sensor provided with the photoelectric converter and used in an image reader, and a signal reading circuit.
2. Description of the Related Art
FIG. 9 is a circuit block diagram of an image sensor used in a conventional image reader. FIG. 10 is a circuit block diagram of a shift register and light receiving elements for the image sensor. FIG. 11 is an equivalent circuit of the light receiving elements. FIG. 12 is an operation timing chart of the image sensor.
As shown in FIG. 10, the image sensor changes resolutions by switching connections of the shift register based on a MODE signal. Further, as shown in FIGS. 11 and 12, at a low resolution mode, the image sensor simultaneously reads plural pixel signals into a common signal line. When the resolution is 1/2 for example, the image sensor simultaneously reads two pixel signals into the common signal line (see JP 11-234473 A: pages 7 to 11 and FIGS. 1 to 4).
However, such a conventional image reader requires many elements to form a switching circuit for switching data signals and has a problem of increase in chip area. In particular, when three or more kinds of resolutions are switched, still more elements are needed for switching data signals. Also, when signals of plural light receiving elements are simultaneously read into the common signal line, offsets of amplifiers for amplifying an output of each light receiving element differ from each other, so levels of signals to be read vary depending on resolutions. Thus, a problem occurs in that a circuit for correcting the variation is necessary.